2-(Thiocyanomethylthio)benzothiazole, TCMTB, is known to be useful in controlling bacteria and fungi in various aqueous systems. The preparation and use of 2-(Thiocyanomethylthio)benzothiazole as a microbicide and a preservative is described in U.S. Pat. No. 3,520,976, as well as in U.S. Pat. Nos. 4,293,559, 4,866,081, 4,595,691, 4,944,892, 4,839,373, and 4,479,961, which give examples of the microbicidal properties of 2-(Thiocyanomethylthio)-benzothiazole. The disclosure of each of these patents is incorporated specifically herein by reference. 2-(Thiocyanomethylthio)benzothiazole is manufactured by Buckman Laboratories International, Inc., and sold as Busan.RTM. 30WB, Busan.RTM. 1030, Busan.RTM. 1118 and other products.
Although a good microbicide, 2-(Thiocyanomethylthio)-benzothiazole tends to be ineffective against bacteria under certain conditions, particularly at high pH. Systems requiring high concentrations of 2-(Thiocyanomethylthio)benzothiazole, moreover, are generally uneconomical.
The mixture of 4,4-dimethyloxazolidine and 3,4,4-trimethyloxazolidine has been used as a microbicide in the metalworking fluid industry for a long period of time. This mixture is sold by many companies as Bioban.RTM. CS 1135, Cosan.RTM. 101, etc. These compounds and the mixtures thereof are known in the trade as "oxazolidines".
As can be seen in Examples 1, 2 and 3, Table 1 (see Samples 13-15), Tables 2 and 3 (Samples 14-16), high concentrations of the mixture of 4,4-dimethyloxazolidine and 3,4,4-trimethyloxazolidine can be required to control both bacterial and fungal growth in metalworking fluids.
Both TCMTB and oxazolidines are used alone to control microorganisms in industrial fluids. Many industries, such as the machining industry, experience problems caused by microorganisms. Aqueous metalworking fluids or cutting fluids used in the machining industry are particularly susceptible to fouling caused by microorganisms. In machining operations, metalworking fluids are used primarily to reduce friction and heat, thereby reducing wear and prolonging the life of equipment.
Metalworking fluids have properties which are ideal for the growth of bacteria and fungi. Although bacteria are important in the biodeterioration of metalworking fluids, fungi and yeast play an important role as well. (Bennett, E. O., "The Deterioration of Metalworking Fluids", Prog. Industrial Microbiology, 13:121 (1974)).
Disadvantageously, these microorganisms can cause the buildup of slime/microbial deposits on machine surfaces, the clogging of jets and lines, the deterioration of the properties of the metalworking fluid itself, enhanced corrosion, and health and odor problems. When deteriorated by the growth of microorganisms, the metalworking fluid loses many of its essential properties. The pH of the fluid may drop and other chemical changes may occur until the fluid can no longer provide adequate lubrication. At this point, the fluid must be replaced with fresh fluid, which is costly and results in lost production time.
The problems associated with the growth of microorganisms have resulted in the extensive use of biocides in metalworking fluid systems. Biocides may be incorporated in fluid concentrate or added to diluted fluids once they are in the holding tanks of the machine works.
There are commercially available biocides. However, many commercially available biocides have odor problems, or create hazards with respect to storage, use or handling, which problems can limit the utility of the biocides. Consequently, workers in the trade have continued to seek improved biocides.
Economic factors, particularly the cost of the biocide and the expense of its application, can also be important when choosing a particular biocide for use in metalworking fluid systems. The cost performance index of any biocide is derived from the basic cost of the material, its effectiveness per unit weight, the duration of its biocidal or biostatic effect in the system treated, and the ease and frequency of its addition to the system treated.
Workers in the trade have sought a commercially available biocide capable of exhibiting a prolonged biocidal effect at economical use levels. Physical conditions such as temperature and chemical reactivity with ingredients present in the system often diminish or eliminate the effectiveness of known biocides. For example, many systems contain organic material which may react with a biocide and render it ineffective.
Metalworking fluid systems in which heavy microbial growth occurs can benefit from the practice of the present invention. The practice of the present invention can also benefit many other aqueous systems, whether or not heavy microbial growth occurs, because the present invention can provide a more limited use of the biocides.